Relief valve for unfired pressure vessels



April 7, 1936. w BRADLEY ZMBQEQI RELIEF VALVE FOR UNFIRED PRESSUREVESSELS Original Fild June 28, 1933 3 Sheets-Sheet 1 7Q 30 19 B ifi 60 93@ AQ/ w J fl flF'ji. j 25 mm a HHHIHH HHII} 3 B6 i 3 e0 19 50 30 30 '7if 7 32 1/ a2 21 pfil 7, 1% I T. W. BRADLEY 23336391 RELIEF VALVE FORUNFIRED PRESSURE VESSELS Original Filed June 28 1930 3 Sheets-Sheet 2April 1, 1936.

T. W. BRADLEY 2,036,391

RELIEF VALVE FOR UNFIRED PRESSURE VESSELS Original Filed June 28 1959 3Sheets-Sheet 3 Patented Apr. 7, 1936 UNITED STATES RELIEF VALVE FOBUNFIRED PRESSURE VESSELS Thomas W. Bradley, Philadelphia, Pa.

Application June 28, 1930, Serial No. 464,510

Renewed ctober 5, 1935 17 Claims. (01. 137-53) This invention relates torelief valves and more particularly to relief valves which are adaptedto afford relief to unflred pressure vessels. I

The main purpose of my invention is to provide a relief valve which willact to release air or gas under an excess of pressure at normaltemperature, and to release both air and gas or vapor content underpressure due to excessively high temperature.

A further purpose is to provide means for regulating the pressure atwhich the valve will function to release air or gasand to provide meansfor the release of. contents at a given temperature.

A further purpose is to provide a temperaturecontrolled exhaust portwhich will act to release the contents through a restricted area at agiven temperature, and a second means which will act at a highertemperature to release a greater area.

will function to release at a plurality (here three) given degrees ofheat, each one higher than the former and to release through differentareas.

A further purpose is to provide means for destroying one fusible metalexhaust port should it fail to function in time to release a secondfusible metal exhaust port.

A further purpose is to provide fusible metal plugs which will melt atgiven temperatures, to provide means for sealing them within the valvecasing so as to prevent their turning and working loose, and to provideports leading from the outside to the fusible metal parts to enable themto melt'more readily under high temperatures. Av further purpose is toprotect a valve of the character indicated from clogging by dirt anddust. p A further purpose is to cause a dust or dirt I guard to beejected with fusible matter when the 49 temperature rises unduly.

further purpose is selectively to control the temperature to which arelief valve is set, whether separately usedor used in conjunction witha fusible relief device and to seal the valve as set againstinterference with the setting.

A further purpose is to mechanically assist in cutting a. suitablerelief device during the ejecting movement of a valve element andwhether the or not.

A further purpose is to operate the valve by a toggle, using a lateralspring upon it to give greater effective assistance for the retur; ofthevalve to its seat where large valves and high pressures are involved,avoiding closure of the toggle and consequent locking of the valve uponits seat and to so construct the valve and. coacting parts as readily topermit their ejection when the outer- 0 most fusible member isdestroyed,

fusible material be weakened by temperature rise.

A further purpose is to lessen the cost of fusible metal members byinserts of cheaper metals.

A further purpose is to utilize a fusible metal member as an adjustingmeans for the valve spring whereby the tension of said spring can be 5varied by the positioning of the fusible metal member.

Further purposes will appear in the specification and in the claims. v

I have preferred to illustrate my invention by 10 several differentforms only, among many in which it may appear, selecting forms which arepractical and inexpensive and which well illustrate the principlesinvolved.

Figure 1 is any elevation of a preferred form of 15 my valve, shownapplied to a tank of which a fragment only is shown.

Figure 2 is a vertical section through the center thereof.

Figure 3 is a top plan view of Figure 1. 20

Figure 4 is a vertical section similar to Figure 2 showing amodification.

Figure 5 is a similar view showing a further modification.

Figure 6 is a plan view of another design of 25 valve.

Figure '7 is an elevation thereof.

Figure 8 is a bottom view of Figure 7.

Figure}! is a'horizontal section on line 9-9 of Figure 10. 30 Figure 10is a vertical section corresponding to line i0--i0 of Figure 6.

Figure 10a is a fragmentary sectional showing an alternate construction.

Figure 11 is a horizontal section on line "-41 35 of Figure 10.

Figure 12 is a plan view of a. similar valve where higher pressures areto be taken care of.

Figure 13 is a section on line 13-13 of Figure 12.

Figure 14 is a horizontal section on line ll-il of Figure 15. 5

Figure 15 is a vertical section on line li -ii of Figure 13.

Figure 16 is a detailed vertical section of the 45 top of a valve casingshowing an adjustable fusible metal member with a reinforcing metalinsert.

In the drawings similar numerals indicate like parts.

My invention is primarily intended to be applied to unflred pressurevessels of which many and greatly variant types exist.

For the purpose of example only, and to illustrate their variantcharacterI might suggest that my invention is also suitable for use incon- 55 junction with grease tanks used in garages and filling stationsfor high pressure service, ammonia tanks in refrigerating plants, aircompressor receivers and discharge lines, acetylene tanks and heaters.

view

'The pressure per cubic inch in these vessels may become very high andthe danger of explosion in case of fire is very great. It-will be quiteobvious to anyone familiar with this art that the invention isapplicable to any vessel carrying a high pressure and which may besubjected accidentally or otherwise to excessive heat.

Figures 1 to 3 illustrate a preferred form of valve wherein l4 indicatesa fragment of the top of a tank, and IS the outer casing of the valveproper, which is cylindrical in horizontal crosssection and is threadedinto the vessel at l6.

The top of the casing I5 is initially open and is provided with a seat Il, into which is fitted a perforated fusible disc I8. This disc' may besealed in place by a slight fianging of the outer. casing as shown at l9or otherwise, as seen in one form, Figure 16, and is further providednear its outer edge with a series of openings 20.

The fusible disc I8 is centrally perforated to support a screw-threadedshaft 2| which carries a spring-adjusting member 22 within a coil spring23.

The upper end of the spring 23 bears against the under side of thefusible disc l8, and the opposite end against a ball or other valvemember 24 closing against a seat 25 in a metal plug 26, preferably offusible material.

This plug 26 may be held within the casin It by a flange 26' upon thebottom thereof, seated within a corresponding groove in the casing, andis provided with a passage 21.

In practice the shaft 2| is turned with a screw driver until the springsupporting member 22 is in a position to cause the spring 23 to exertthe desired pressure. It is then sealed in place at 33.

The fusible disc I8 is weakened by the closeness of the perforations asindicated at I 6' of Fig. 3. The perforations permit flow of gases (dueto excessive pressure) even in the absence of temperature rise. They arearranged in circular form.

It is the purpose to so proportion the size of openings 20, thicknessandfusingtemperature of the fusible disc IS, the small or largerconnecting web of metal l8 between the perforations, to the size of theopening- 21, the thickness of the metal of the plug 26 and the fusingtemperature at which this plug 26 is intended to weaken, in order thatone of these fusible elements will go before the other.

I plan to have the disc l6 weaken and discharge prior to the weakeningand discharge of the plug 26, and, therefore, correspondingly adjust thenumber, size, stiffening efiect, thickness and temperature of melting ofthis disc l8, so that with rise in temperature fluid will be releasedfully through it before release of the plug 26.

In order that my device may be affected by temperature within the room,as well as by the temperature of gases or vapors within the vessel (asan additional fire protection) I provide openings 30 about the disc l8and/or openings 3i (Figure 4) about the plug 26 to permit access offlame directly to the fusible material in case of outside fire.

The adjusting member 22 is preferably applied in the form of a nut uponthe shaft 2| and the shaft is retained against movement in an upwarddirection by a collar 32 pressing against the lower end of the disc, or(if it be desired to prevent movement in both directions) by a collar 32located within the metal of the disc as shown in Figure 5.

In either case after adjustment has been made the space between the topof the screw and the upper part of the disc I8 or iii may be filled byfusible metal 33 to prevent alteration of the setting.

Much of my invention applies without regard is whether the adjustingmechanism for the spring strength be used or not and the device has beenillustrated free from the adjusting mechanism in Figure 4 to point outthis fact.

Figure 5 is shown for the purpose chiefly of iilustrating the capabilityof adjusting the spring either by compressing the spring above the nutto allow further expansion of the portion of the spring below or byforcing the spring below the nut down to give additional compression ofthis spring. In Figure 2 adjustment of the compression of the springbelow the nut alone is permis sible.

Since there can be no tension of the spring between the nut 22 and thevalve the only adjustment which can be made is one of extent ofcompression of that portion of the spring lying between the nut and thevalve. In the form of Figure 5 it is possible to compress additionallythe portion of the spring lying between the nut and the head of thescrew, reducing the normal extent of compression of the part of thespring between the nut and the valve. With reverse movement of the nutthis portion of the spring between the nut and valve can also beadditionally compressed. In the form shown in Figure 2 this additionalcompression is the only adjustment that can be made.

It is advantageous to have the seat for the valve element (the ball 24)in the soft fusible metal, as the constant pressure on the ball by thespring 23 will cause the ball to form its own seat.

In operation the contents of the vessel, whether viscous, liquid orgaseous is introduced, preferably near the bottom, and the vessel isfilled until the pressure inside reaches that at which the valve isintended to release.

If the content be viscous or liquid, air will then begin to pass outthrough the valve when the intended pressure has been reached. In caseof gas content, mixed gas and air will begin to pass out at the pressurefor which the spring has been adjusted.

The valve will continue to operate under these conditions unless exposedto heat so excessive as to cause expansion within to a pressure beyondthat provided for by the spring. When a high temperature of this kind isreached, disc 18 will soon weaken'and the spring 23, element 22 and wscrew 2| together with the valve 24 will be blown out of the casing andwill permit much more free passage of heated air and content through thepassage 21.

If the temperature be of sufllcient height, the second fusible plug, 26will melt and allow the contents to be ejected through a larger orifice,it being understood that the disc i8 is of larger metal area and hasmore exposed surface than that of plug 26 and may correspondingly bemade always to melt first.

Gas or vapor above the air pressure will lift the valve 24 and will passout through the opening 21 in the plug 26 and through the openings 20.

The question as to which plug will melt first is a composite questioninto which many other elements enter including the ratio of volume ofplug to the surface exposure of hot gases or vapor.

The pressure of the spring 22 is effective to drive the center of thefusible disc l8 out as soon as the fusible material begins to weaken.The pressure of the spring upon the disc l8 will be greater, of course,as the ball is lifted than when the ball is seated and will increasewith the extent to which the ball is lifted.

The openings 3| are desirably larger than openings 30 because of thelarger bulk of fusible material 26 as compared with the disc l8.

Inthe form of my invention shown in Figures 6 to 11 inclusive, lindicates a valve casing, restricted at its lower end and seated withina receptacle 36, threaded at 31 for attachment to a vessel.

A disc of fusible metal I8 is secured in a seat H in the upper end ofthe ,casing and held in place by hanging as shown at IS. The disc isfurther provided near its outer edge with a series of openings 20 topermit the escape of air, and near its center with supporting posts 40to hold a cap 4|.

This cap is supported a sufllcient distance above the disc I8 to permitair to escape freely through openings 20 but is of such shape as tocover the openings above and cover the edges of the casing I5, therebypreventing the accumulation of dust and dirt in the openings 20 The discI8 is further provided on its under side with a centrally located lug 42which forms a support fora screw-threaded shaft 42 which in turn carriesa spring tension adjusting collar 44 surrounded by a coil spring 45. Theupper end of the coil spring 45 surrounds the lug 42 and rests againstthe under side of the disc I8 while its lower end rests upon a ball 24seated at 25 within a fusible metal plug 26. It willpbe seen that thisform, so far as described, is closely similar to the form shown inFigure 2.

The screw-threaded shaft 43 has a collar 42' integral therewith whichbears against the lug 42.

The outer face of the collar 44 is grooved to correspond to theconvolutions of the coil spring 45 which fit therein, as in the case inFigure 2. The fusible metal plug 25 is held within its seat in the samemanner as in Figures 2, 4 and 5.

Carried upon the upper part of the ball 24 and surrounding the coilspring 45 is .a cup-shaped member 41, having a bearing portion 48 in itsbottom to form a seat upon the ball. It carries also a series of smalleropenings 49 to prevent the cup from collecting moisture fromcondensation. The upper periphery of this cup is in line with thecenters of the openings 20 in the disc l8 and is sharpened to a knifeedge 50.

The casing I5 is restricted at its lower end and is held within thereceptacle 36 by a fusible sleeve 5|, seenin Figures and 11. i

In order to prevent the casing from turning within the seat of thereceptacle 36 and thereby working loose, I provide flutes 52 within thecasing l5 and flutes 53 within the receptacle36.

When the fusible metal is poured into the socket it will fill the fluteswith metal as at 54,55. For a like purpose and in order to prevent thewithdrawal of the valve casing vertically from the seat I furtherprovide an annular groove 52' within the casing l5 and another 53'within the receptacle 36 and the fusible metal when poured in its moltenstate forms annular flanges 54' and 55 respectively within thesegrooves.

Receptacle 38 can be parted at 55 to permit heat to reach the fusiblemetal therein more quickly. Likewise it can be parted as in Figure 4 toreach the plug 26 and the disc I8 In operation, the introduction of thecontent to the vessel is the same as in the prior forms, and the ball 24is raised from its seat by the force of the air or gas and is returnedto'its seat by the pressure of the spring below the tension adjustingcollar.

When the valve is subjected to intense heat the disc ll! of fusiblemetal will melt and permit the cap 4|, spring 45, screw shaft 43, ball24 and cup-shaped member 41 to be blown from the casing, and the heatedair and content can escape through the opening in the plug 26.

If for any reason the plug 26 should melt prior to the disc I8 the forceof air trying to escape from the vessel will drive the ball 24 andtherewith the cup member 41 against the center of the perforations inthe disc l8 and the knife edge 50 will cut its way through the thinwebbings between the openings thereby releasing the interior of thevalve structure as above.

Any further rise in temperature will cause the fusible metal within thereceptacle I to melt and release the entire valve casing l5 allowing anunrestricted opening to atmosphere.

It will be obvious that-pressure alone without temperature increasewould be effective if sufficiently high to cause the cup member to cutthe fu:.ible material between the perforations.

If desired the fusible metal in the disc l8 can have a lower meltingpoint than that of the plug 26, while the fusible metal 5| within thereceptacle 36 can have a higher melting point than the plug 26, thusassuring the melting, first of the disc I8 second of the plug 28 andthird of the metal 5|.

It will be further observed that with the removal of the disc I8 theexhaust opening is limited to the area of the port 21. With thedestruction of the plug 26 the area of the opening is increased, andwith the destruction of the fusible metal element-5| a quicker exhaustto atmosphere is obtained.

In Figure 10a I have illustrated an alternate wherein the valve seat forthe ball 24 is in-, tegral with the casing l5 and 'of a non-fusiblemetal. In this form the ball valve works as in all the other forums heredescribed for the discharge of air, but there is but one fusible metalplug, that at the base of the casing, so that when the fusible metalmelts the entire valve is blown out of its seat without destroying theinterior of the valve as in the other forms.

It may be desirable under certain conditions. such as. for example,where largertanks and higher pressures are encountered, to attach mypressure element within the casing in a horlzontal position and combineit with a toggle'motion' to keep the valve closed upon its seat.

I illustrate such a toggle motion in Figures 13, 14 and 15. whereinspring tensioning members are carried which project from the inside ofthe side wall of the casing in line with a break in the toggle motion60. This toggle motion consists of two levers 6i and 62 pivoted togetheras at 63 and having their outer free ends 64 and 65 terminating inballs. The ball on the lever 6| rests within a. socket 65 in the underside of a plate 61 which forms the hard metal part of a composite metalplug, I8 the fusible metal portion being designated at 68. The ball onthe lever 62 rests within a socket upon the upper face of a valve 24".

The spring action uponthe toggle is set to the required tension fromoutside the side wall by turning the threaded shaft with a screw driver.When the desired tension is obtained the driver is removed and the holefilled with a soft metal which tends to maintain the adjusted screw inposition.

From a socket formation ill within one side of the casing i5, I projecta threaded shaft 43" corresponding to the shaft 43 in Figure and to 2|in Figures 2 and 5. This shaft carries a threaded nut 44 having itsouter face conforming to the convolutions of a tension spiral spring45'.

A substantially spherical shaped portion 43 integral with the shaft 43rests within the socket l0 and forms a support for the threaded shaft 43One end of the spiral spring 45 rests against the inside of the sidewall of the casing, is supported near midway of its length by the nut44' and at the opposite end is attached to the toggle motion at itsjoint 83.

The outer free end of the threaded shaft 43 projects to a point where itcomes in contact with the toggle, which prevents the two arms GI and 62from assuming a perpendicular position. This would cause the toggle tolock.

The spring 45' holds the toggle 60 under constant tension, tending toforce the valve 24 closed upon its seat 25', which is formed within afusible metal plug 26 apertured at 21'.

The valve is guided within the aperture by a ribbed projection 24depending from its under face and riding within the walls of theaperture 21. The valve is further guided by rods 1| carried by ears l2projecting from the upper face of the valve 24. The outer free ends ofthe rods ride within grooves 13 formed within the side walls of thecasing and extend from the line of the valve seat 25' upwardly to apoint in line with the bottom of the plate 61. The upper ends of thegrooves are open as at 13' to permit the insertion and ejection of theguide rods II.

The composite metal plug 18 has a central portion 61 and is surroundedby a P rforated fusible metal portion 68, the perforations beingdesignated at 68 The central portion has an annular groove 61' intowhich the fusible metal portion is moulded, thereby assisting in lockingthese two metals together.

In the form of my invention illustrated in Figure 16, I have shownpractically a duplication of the upper portion of Figure 4, thedifference being I have internally threaded the casing i5 and externallythreaded a composite plug I5 to fit therein. By using the openingsnormally intended for the escapement of air or gas under pressure, forthe insertion of a spanner wrench, I can raise or lower the plug andthereby vary the tension of the spring 23. When this is done enoughaxial pressure should be brought upon the plug to nearly balance thespring pressure so as to relieve the threads from excessive wear.

In operation, the valve is raised from its seat by the pressure of airor gas within the vessel, (causing the toggle to open against the springtension) and is returned to its seat by the action of the spring whichtends to straighten the two arms GI and 62 .of the toggle motion andclose the toggle.

The valve is guided to its seat from below by the ribbed projection 24and from above by the guide rods ll riding in the grooves 13 in the sidewalls of the casing.

The valve continues to function in this manner as long as thetemperature surrounding the valve is not excessive. If excessive heat beencountered, thefusible metal portion SI of the composite plug 61 willmelt, and the hard metal part will be raised by the action of thetension spring tending to straighten the toggle and bring it into aperpendicular position.

when the toggle straightens the free end of the threaded shaft 43 willbe raised also, due to the connection of spring 45' with the toggle,tending to unseat the substantially spherical portion 43 of the shaft 43and help to position it for ejection.

With the parts in the above position and with the air or gas pressureseeking to escape, the valve 24 will be forcefully raised from its seatand all the elements connected with it, i. e. the two toggle arms SI and62, the plate 61, the tension spring 45' and shaft 43* together with thenut 44' will be ejected from the casing, allowing the air or gas toescape through aperture 21.

As the parts leave the casing they are guided by rods 'Il travelingwithin grooves 13.

Any considerable further increase in temperature will cause the fusiblemetal plug 26 to melt, thereby creating a much larger opening for theescape of the air or gas under pressure.

In view of my invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part of the benefits of myinvention without copying the structure shown, and I, therefore, claimall such in so far as they fall within the reasonable spirit and scopeof my invention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patcut is:---

1. In a relief valve, a casing having a valve seat facing away from thepressure end of the casing, a valve engaging the seat, an aperturedfusible plug at a distance outside of the seat, a spring restrained bythe plug and holding the valve to its seat whereby pressure free fromhigh temperature will lift the valve and discharge through the apertureand with increased temperature will discharge the valve and spring alongwith the fusible element.

2. In a relief valve, a casing having a valve seat of fusible metalfacing away from the pressure end of the casing, a valve engaging theseat,

an apertured fusible plug at a distance outside of the seat, a springrestrained by the plug and free from high temperature will lift thevalve and discharge through the aperture and with increased temperaturewill discharge the valve and spring along with the fusible element.

3. In a relief valve, a casing, a perforated fusible metal disc fastenedwithin the casing, a fusible metal plug fastened within the casing andhaving a passage therethrough with a valve seat at its upper end, avalve normally within the seat, and a coil spring interposed between thevalve and the perforated metal disc to keep' the valve normally in itsseat.

4. In a relief valve, a casing having a valve seat of fusible metalfacing away-from the pressure end of the casing, a valve engaging theseat, an apertured fusible plug at a distance outside of the seat, ascrew bearing against the fusible plug, a nut adapted to be advanced orretracted by the screw, 2. spring, connection between the nut and thespring whereby the pressure of the spring against the valve isdetermined by the positioning of the nut on the screw. and whereby (illpressure free from high temperature will lift the valve and dischargethrough the aperture and with increased temperature will discharge thevalve, the screw and its nut and the spring together with the fusibleelement.

5. In a relief valve, a casing having a valve seat of fusible metalfacing away from the pressure end of the casing, a valve engaging theseat, an apertured fusible plug at a distance outside of the seat, aspring restrained by the plug and holding the valve to its seat wherebypressure free from high temperature will lift the valve and dischargethrough the aperture and with increased temperature will discharge thevalve and spring along with the fusible element.

6. In a relief valve, a casing, a spring-pressed valve member openingaway from the pressure end of the casing, a fusible metal discrestraining the spring of the valve and apertured for exhaust of gasunder pressure and a cap attached to the disc protecting the disc fromforeign matter and by reason of the gas discharge bringing additionalpressure on the disc to cause it to'be expelled.

7. In a relief valve, a casing, a spring-pressed valve adapted to openaway from the pressure end of the casing, a weakened disc holding thespring andapertured to allow gas to pass through it under pressure, anda cutter for the disc engaged by the valve and under excessive pressureadapted to be pressed against the disc by said valve.

8. In a relief valve, a casing, a fusible disc near the outer end of thecasing apertured for passage of air and gas under pressure, aspring-pressed valve inside of the casing having the spring tendingto,expel the disc, a cap over the disc adapted with the discharge of gasto additionally strain the disc outwardly, and a cutter forthe disccarried by the valve and adapted to engage the disc with excessive valveopening. I

9. In a relief valve, a body having a valve seat at its inner end, avalve engaging the seat, a perforated member at the outer end of thebody adapted to weaken with increase of temperature and permittingpassage of air and gas through the perforations, and a spring-extendedtoggle connection between the valve which engages the seat and theperforated member, bringing the toggle pressure upon the member to beheatweakened and adapted to be blown from the body when the perforatedmember gives way.

10. In a relief valve, a body having a valve seat at its inner end, avalve engaging said seat, a

perforated member at the outer end of the body an adjustment for thestrength of the spring tending to straighten the toggle.

11. In a relief valve, a body having a valve seat at its inner end, avalve engaging said seat, a perforated member at the outer end of thebody adapted to weaken with increase of temperature and permittingpassage of air and gas through the perforations, a spring-extendedtoggle connection between the valve which engages the seat and theperforated member, bringing the toggle pressure upon the member to beheatweakened and adapted to be blown from the body when the perforatedmember gives way, and an adjustment for the strength of the springtending to extend the toggle, the adjustment being accessible from theoutside.

12. In a relief valve, a body having a passage through it, aheat-weakened apertured member near the inner end of the body providinga valve seat and destructible with high temperature, a valve engagingthe seat,'a second heat-weakened apertured member within the passage ofthe body permitting normal discharge of air and gas through theapertures, a toggle engaging the valve and heat-weakened member, and aspring engaging the toggle and adapted to cause the toggle tostraighten, the toggle being set in position so the valve can be forcedopen against the spring.

13. Ina relief valve, a body having a springclosed valve therein and anapertured composite fusible member beyond the valve, the compositemember comprising fusible apertured material about the outer part and anon-fusible core to receive the pressure of the spring.

14. In a relief valve, a tubular body, an apertured fusible memberthreaded into the outer part of the body and adjustable by the thread tovary its position, a valve seat in the inner end of the body, a valvecooperating'with the seat and a spring in the tubular body toward theouter end of the body from the valve seat, contacting the fusible memberat one end and the valve at the other end.

15. In a relief valve, a tubular body, an 'apertured fusible memberthreaded into the outer part of the body, adjustable by the thread tovary its position, and a spring pressed valve construction within thetubular body, located wholly toward the inner end of the body from thefusithe non-fusible part of the composite fusible 010- sure.

17. In a relief valve, a tubular casing having an internal passageadapted to communicate at one end with a chamber to be protected, afusible plug forming a valve seat within the casing near the endcommunicating with the chamber, a valve adapted to engage the seat, asecond fusible plug extending across the end of the passage away fromthat in communication with the chamber and apertured to pass gas or airunder pressure when the valve is lifted and a spring urging the valvetoward closure, supported by the second fusible plug and adapted to beblown out bodily in case of fusion of the second fusible plug.

THOMAS W. BRADLEY.

